How does potassium balance out sodium in maintaining a person’s blood pressure? I’ve read that it has something to do with osmosis across the cell membrane.
In: Biology
Renal physiologist here.
A lot of evidence is showing that increased potassium intake can help hypertension by lowering sodium in the body. It actually comes as a bit of a surprise, because high potassium elevates aldosterone, a hormone that results in getting rid of potassium in the kidneys but also promotes the reabsorption or retention of sodium. But you can’t argue with evidence.
The mechanism with how this works remains unclear. The most prominent hypothesis for now is that potassium can downregulate or reduce the NCC (sodium chloride cotransporter). I won’t get into the molecular mechanism, but it has to do with the voltage or potential across the cell membrane altering chloride in the cells.
Many non renal mechanisms have also been proposed. Quoting a study directly, these include reduced renal renin release (a hormone axis regulating blood pressure), decreased vascular smooth muscle cell proliferation (reduce muscle cells in the blood vessels, which normally function to constrict the vessels and elevate blood pressure), reduced vascular smooth muscle cell migration, decreased free radical formation, reduced low-density lipoprotein cholesterol oxidation, decreased platelet aggregation, and improvement of endothelium-dependent vasodilatation and reduction of oxidative stress. I didn’t explain how some of these mechanisms can lower blood pressure because they’re quite complex and quite indirect. Some even proposed that the sodium potassium pump may be at play for this antihypertensive effect: this pump is found almost everywhere and it extrudes or pumps out 3 sodium ions out of cells while taking in 2 potassium ions. If you increase potassium on the outside, you’d shift the balance towards more sodium leaving cells, and in the big picture, leaving the blood and body. But of course it’s not so simple, and altering the Na-K pump has heavy functional implications too that affect blood pressure in more complex mechanisms.
So TL;DR: we are becoming increasingly more certain potassium lowers blood pressure, but we’re not sure how. It’s unlikely to be a simple osmotic mechanism but rather a multi faceted functional one that involves direct and indirect effects.
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